And I will never forget how, on the day before she returned to late-night television as a guest on Letterman’s Late Show after 27 years in the post-Johnny chill, Joan wouldn’t let the segment producer off the phone until she could tell him about a young comedian named Billy Eichner. “He’s absolutely brilliant. You have to have him on the show,” Joan insisted to a producer assigned to find out what jokes Dave would need to set up for her the following day. “Billy Eichner.” She repeated. “He’s hilarious. I’ll bring you a DVD.” And the next afternoon, in the middle of all of her frantic preparation for what would be her big, nerve-wracking, triumphant return to the Ed Sullivan Theater — where she debuted as a 33-year-old on a show that preceded Dave’s — she did bring a DVD of Billy’s YouTube clips to personally hand to that very producer. Billy, by the way, will be appearing on Letterman next week for his first time. Somewhere, she’s kvelling.